Cathode ray tube



Feb. 25, 1941. K. SCHLESINGER cun1m RAY TUBE Filed Nov. 5, 1938 Inven/ar Kvrt .3c/aesinger Pafentecl Feb. 25, 1941 UNITED STATES PATENT OFFICE CA'IIIODE RAY TUBE Application November 5, 1938, Serial N0. 239,154

- In Germany April 5, 1938 9 Claims.

The invention relates to improvements in the electron-optical arrangement, more partieularly for Braun tubes of high output, in which a. diaphragm aperture acta as object f reproduction and a so-called intersection-point optical system is employed.

I1; has already been proposed by the applicants on a previ0us occasion to use 1ar'e-surface cathodes in conjunction with a net-like control 0 grid, in order in this way considerably to increase the properly controllable intensity of the ray current. The realisation cf this idea is confronted by difficulties in the electron-optical treatment cf the electronic ray. II: has been ob- 15 served that the image point on the screen has always been considerably 1arger than was 120 be expected on the basis of the simple laWs of elactron-optica'l reproduction which have been'employed heretofore and up to now have been found to be sufiiciently accurate. The reason for this difference is due only in part to the natura of the electron-optical systern employed which theoretically can be controlled only with difliculty. For the other part, as experiments have 25 conclusively shown, it must be laid down to errors of reproduction an the part of the electronic lenses. Generally speaking, the main lens 15 incapable of uniting in the same point as the rays which are near to the axis the rays which 30 are remote from the axis and the direction of which forms wlth the axis a comparatively large angle. In consequence there is a deformation and an increase in the size of the image point, which in unfavourable circumstances may even 35 go so far that subsidiary images am produced, i. e., that, in place of one image point several of these appear on the screen. The reason for this latter effect has been found to consist in the fa.ct that the preliminary concentration sys- 40 tem is incapable of handling marginal rays which f0rm anexcessively large angle with the axis. Furt;her there are frequently observed apprecia.ble halo effects, which are due to the considerable formation of secondary electrons at the edge of the diaphragm in the case of great intensity 01 the ray current. II; is the object o-f the invention to eliminate the image errors referred to.

The electron-optica1 arrangement according to 50 the invention is illustrated diagrammatically by way of example in Fig. 1. The preliminary coucentration system, which unites in the aperture of the diaphragm acting as object 015 reproductlon all rays which pass through the contro1 grid, 55 is formed by the diaphragm I, I:he aperture-lens electrode I anal the cathode Ii. According to the invention, there is provided in front of the diaphragm I an electrode 8 which is raised to the same potential as the diaphragm and is prefer ably united by means 0f an annular intermediate 5 member With the diaphragm itse1f to form a. single metallic diaphragm element. The inlet aperture 0 of the diaphragm element determines in conjunction with the spacing c between the electrodes 8 and I the angle of entry o: of the 10 ray into the diaphragm, or into the lens space situated behind the same, and serves to shade off interfering, excessively inclined marginal rays. The aperture electrode I may 11012 be employed as diaphragm, as otherwise marginal errors will again unavoidably occur. Its opening must always be somewhat larger than I:he crosssection 0f the electronic ray traversing the same.

In order as far as possible to render harmless the heat developed by impact of the electrons the diaphragm I is formed by a thick metallic disc having a conic'al recess at its centre. The actual diaphragm aperture is located in a thin sheet of p1atinum, which is welded on 110 the rear of the metallic ring.

According to the invention, the main lens sonsists of an inlet tube 2, which has a lower potentia1 than the diaphragm, and an outlet tube 3, which is raised 130 anode potential anti is preierably metallicly connected with the anode 4. AI: the Same time, according to the invention, the diameter of the outlet tu.be is selected to be approximately uns-half of the diameter 0f the inlet tube. The outlet tube extends for approximately one-half of its length into the inlet tube.

According to an additional feature cf the invention, there is introduced into the interior of the cylinder 2 a further perforated diaphragm I4, spaced to such extent from the lens field that interference With this field by the diaphragm I4 is out of the question, i. e. at a distance 0f aI; least 2-3 times 01. The size of the opening I4 is such tha)t all rays passing through the same enter the main lens within an angle amounting to 8090% of that determined by 01. In this way rays which are extremely remote from the axis 8.11C1 cannot be properly embraced by the main lens are precluded. On the other band the effect; of the diaphragm I4 is obtained all the more readily the more it is spaced away from the main diaphragm.

The connecting of the tube in accordance with the invention is particularly important. The anode 4 is connected with the highest positive potential, the tubular lens electrode 2 with a low adjustable focussing potential The bias of the diaphragm I can be adjusted as desired at the point 9 of a potentiometer.

In the case of variation 01 the diaphragm bias there occurs the following: If the bias 0f the diaphragm I is increased until it gradually reaches the ful1 anode potential, the energy in I:he Image point is increased considerably with approximately constant density of ene1gh i. e., the diameter o-f the image point also increases. Accordingly by varying the tapping 9, the size of the image point, with constant and wel1 defined form of the lurninous spot, can be so 213djusted that the lines just overlap. It. is an attendant feature of the arrangemen-t as described that, without special means, a consiclerable fraction of the oncoming electronic current is swal-- lowed up by the diaphragm itself. In consequence the bias of the diaphragm varies in a. manner dependent on the medium image current. These fluctuations in the potential of the diaphragm, however, do not make themselves noticeable in the form of impaired sharpness of the Image point, but only as a practically negligible variation in its size. Smoothing means for the diaphragm can accordingly be dispensed with.

Owing to the varying current reception 011 the part of the diaphragm I, however, there also varies at the same time the bias o-f the 1ens eleetrode 2. Each variation in the potential cf this electrode, however, makes itself immecliately noticeabie by lack of sharpness of the image. Gare must accorclingly be taken that potential fiuctuations of the tuoe 2 are prevented.

Tests have shown that the cylinder 2 remains practically free from current reception entirely so long as the bias of the diaphragm element I/8 is positive in relation to the bias of the cylinder. There results from this a simple method of maintaining the potential of the electrode 2 constant during the operation of the tube. Ac-

cording to the invention, smoothing elements.

III] I I are connected in the lead to the electrode 2. At the same time the time constant of this combination must be grea.ter than the image change period in oraler to avoid that the sharpness of the point is afiected. by the contents of the image. Ther'e can be employed a comparatively high resistance III (approximately 0.5 to 1 megohm), and a -cpmparatively small co-ndenser II (approxixnately 01 u F.) is then suztficient. It may b e established at this point that against all expectations the smallest sharp Image po-int capable of being obtained at thescreen 5 has the size resulting from the simple 1aW of spacing, and tha.t all image points which are obtained by-increasing thebias of I beyond the bias of 2- are larger than this extreme value.

Of particular importance in the selection. of the concentration system is the spacing a between control gricl and electrode I and the spacing c between diaphragm I anal electrode 8. As already shown above, the diaphragm element 8 determines the angle a at which the bundle of rays enters the tubular space after traversing the concentration field. There must accordingly be maintained approximately the proportion o:c=oul, 01' being the size of aperture of the outlet cylinder 3 anal Z the spacing 1, 4. The spacing a determines together with the quotient of the potentials at I and 8 the scale by Which the cross-section of the ray is reduced from the cathode Ii'-up to the diaphragm l. In this connection, if b {S th'e spacing between I anti. 8, the

distance b+c as image width isof a praotically fixec'l nature. Experiments have shown the most favourable sca1e of reduction to have a value o-f approximately 5:1. Since experiments have also shown that the most favourab-le potential distribution for the electrodes of the concentration system isfixed Within comparatively narrow limits, the said spacing a and also: the greatest cathode surface capable of being utilised are by reason of the electron-optical law cf reproduction also of a definitely fixed Kind.

Acco-rding t0 an additional feature of the invention, the net electrode I5 acting as control gridis itse1f clesigned as diaphragm by the fact thatits aperture is made equal 130 the cathode surf'ace capable of being utilised or oniy very little larger. In this manner there is prevented at the outset the occurrence of marginal rays which are so greatly inclinecl in relation to the axis that they coul d in no case be properly handled by the concentration optical system.

The net should divide the cathode surface into at least 10, and preferably more, elementary areas. With. a cathocle diameter 01 1.5 mm. anal. agrid. constar'1t of 0.5 mm. 9 gridwi1idows can be obtained.

Fig. 2 shows as an additional feature of the invention an arrangement with Which it is possible to ma-ke the diaphragm I itself currentless, am]. at the same time.to prevent a halo= efiect in thevicinity of the image point caused by secondary electrons. In this case. the diaphragm. l preferably has the s'ame potential as. the tubulai member 2, With which it. can be metallicly connected. On the inIet side of the cathode ray there is located a speoial aperture-electrode I3, whichas -comp'ared with the diaphragm is raised to a. potential wl'iich is positive: to the-extent of a few hundred volts. The spacing between I3 and I is preferably o-f the order of the aperture of I3. Both amount to approximately 1 mm. Im-- mediately the electrocle I3. hasa potential which is at least 100 volts higher than the diaphragm the di-aphragm circuit is without current.

The explanation for this efiect is so be found in the secondary emission occurring at the edge of the diaphragm, for which emission in the case o1" potentials of more than 200 vol.ts the ratio S:P is already greatter than l, an.d certainly, therefore, in t he case of those. potentials with Which cathode ray tubes are operated. The bias of the electrocle I3 can accordingly be adjusted. in such fashion that the 1oss current of the diaphragm is immediately again compensated by seconclziry emission currents.

It has been found that the electrode I3 is capable of completely replacing in efiect the electrode 8 in Fig. 1 so that the latter is superfluous.

Ae0mioination of this Rind comprising a suctional electrode I3. and an aperture diaphragm I can be employed' in allcases in Which elimination of the current loss of the diaphragrn is desired. The provision of. the. emotional electrode on the inlet side of the cathode ray has the advantage that the secondary emission isabsorbed bef0ref the secondary electrons ente-r the space of the main 1ens. In this way the image point is freed from its interfering halo.

What I claimas new anal desire to secure by Letters Patent ist l. A. cathode ray tube comprisihg means ineluding a cathode for produeinganal conti*olling a.- cathode ray, a first aperturei di'aphragm, a concentratingel'ectroxr optica1 system compris'ing tW'o-further diaphragr'nsifox fcusing said cathod ray in the aperture cf said first diaphragm, an intensity control ele ':trode arranged between said cathode and said concentrating system and cousisting of a fine-wire net supported by another diaphragm, the aperture of whlch hasapproximately the same size as -the emissive surface of said. cathode, a luminescent screen, and. a further elecbron optica1 System for reproducing the aperture of said first diaphragm on said screen, all of said diaphragms having aperture's 'lahe diameters of which decrease inversely proportional 170 the distance of sa.id diaphragms from said control electrode, said. second electron. optical system comprising a first cylinder am]. a second cyl1nder mounted co-axially with said first cy1- inder and extending to the space between said first 1cy1inder and said screen, said' second cy1- inder having a diameter of approxlmately of the diameter of said first cylln'der and extending into said first cylinder for approximately A; of its 1ength.

2, A cathode ray taube comprising means inc1uding a cathode for produclng a cathode ray,

an intensity contro1 electrode m0-unted in front of the emissive surface of said cathode, a. first apertured. diaphragm, an electron optica1 preconcentrating system adapted to produce a first focus of said cathode ray in the aperture of said: first diaphragm, saicl preconcentrating system consisting cf said first di'aphngm and two further apert;ured diaphragms mounted between said first diaphragm and said control electrode, the intermediate cf said three diaphragms having a smaller distance from said first diaphragm than from the third of said diaphgrams, the ap ertures of said. three diaphragms having decreasing diameters in the direction from sa1d cathode, the size cf the aperture of said first dlaphragm being approximately equal to one fifth oi the size cf the active emissive surface of said cathode.

3. A cathode ray taube comprising means including a cathode for producing a cathode ray, an intensity control electrode mounted. in front of the emissive surface of said cathode, a first apertured diaphragm, an electron optica1 preconcentrating system. adapted 1:0 produce a first focus of said. cathode ray in the aperture of said first diaphragm, said preconcentrating system consisting 0f said first diaphragm anti two further apertured diaphragms mounted between. said first diaphragm and said contro1 electrode, the intermediate of said three diaphragms having a smaller distance from said flrst diaphragm than from the third of sa'1d diaphrag ms and being electrically connected with said first diaphragm.

4. A cathode ray tube comprising means including a cathode for producing a. cathode ray, an intensity control electrode mounted in freut of the emissive surface of said. cathode, a f1rst apertured diaphragm, an electron optical preconcentrating system adapted 110 produce a first focus of said cathode ray in the aperture of said first diaphragm, said preconcentrating syst;em consisting of said first diaphragm and two further apertured diaphragms mounted between said first diaphragm and said. control electrode, the intermediate of said three diaphragms having a smaller distance from said first di-aphragm than from the third of said. diaphragms and being electrically connected with sald first diaphragm, the apertures of said three diaphragms having decreasing diameters in the direction from said cathode, the size cf the aperture of said first diaphragm being approxima'cely equal 1:0

one fifth cf the size of the active emissive surface of said cathode.

5. A cathode ray taube comprising means inc1uding a cathode for producing a cathode ray an intensity control electrode mounted in front than from the third of said diaphragms, the' apertures of saidi three diaphragms having clecreasing diameters in the direction from said. cathode, the size of the aperture: of said. first diaphragm being approximately equal 120 one fifth of the size of the active emissive surface of said cathode, said control electrode consisting of a fine-wire net supported. by a further diaphragm the aperture 01 which has approximately the same size as the active emissive surface of said cathode.

6. A cathode ray tube comprising means including a cathode for producing a cathode .1ay, an intensity control electrode mounted in front of the emissive surface of said cathode, a first apertured diaphragm, an electron optica1 preconcentrating system adapted to produce a. fi1st focus of said cathode ray in the aperture of said first diaphragm, said. preconcentrating system consisting cf said first diaphragm and two further apertured diaphragms mounted between said first diaphragm and said control electrode, the intermediate of said three diaphragms having a smaller distance from said first diaphragm than from the third. 0f sa'1d diaphragms, the apertures of said. three diaphragms having diameters decreasing substantially inversely proportional to the distance of said diaphragms from said control electrocle, the size cf the aperture of said first diaphragm being approximately equa1 to one fifth o-f the size of the activa emissive surface of said cathode.

'7. A cathode ray tube comprising means including' a cathode for producing a cathode ra.y an intensity control electrode mounted in front 015 the emissive surface of said cathode, a. first apertured diaphragm, an electron optica1 preconcentrating system adapted to produce a first focus of sa'1d cathode ray in the aperture of said first diaphragm, said preconcentrating system consisting of said first diaphragm and two further apertured diaphragms mounted between said first diaphragm and said control electrode, the intermediate of said. three diaphragms having a smaller distance from said first diaphragm than from the third of said diaphxagms, the apertures of said. three dia.phragms having diameters decreasing substantially inversely proportional to the distanee of said. diaphragms fxtom said contro1 electrode, said control electrode consisting' of a further -diaphragm having a central opening of approximately thesame size as the active emissive surface of said cathode, the size of the apertum of said first diaphragm being approximately equal 130 one fifoh of the size of the acoive emissive surface cf said cathode.

8. A cathode ray tube comprising means including a cafuhode for producing a caohode ray, an intensity control electrode mounted in freut of the emissive surfaca of said cathode, a first apertured. diaphragm, an. elec.tron opticali pre= concentrating system adapted to prod'uce a. fl.rst foeus of said cathode ray in the: apenture of said first diaphrag-m; said preconcentrating system consisting of said fi'rst diaphragm andxtwo further apertured diaphragms mounted between said first diaphragm;a.nd said oontml electrode, the intennediate. of said' three diaphragms having au. sma;ller distancefrom saicl. first diaphragm than from the thi1d. 0f said diaphragms, the aperturesof: said thnee diaphra.gnw having de.-

creasing diameters. in. the direction fromsa1d cabhode;.the s1'ze. of: the a.perture of saic'l first diaphragm being a;pproximately equ=a1 120 one fifth0ff the size of:the. activeemissive surfacez. 0f

said cathode;y said.first =diaphra;gm being :t0rmed by a: solid; plno-pamllel metalli'c disc having a conical: recess a.t: its centre, the smallery end 0f said rec'zess being. covered.eby mthin.sheet bf platzinum havingya ce ntTal;opening.

9. A; cathode ray taube:- comprising means= including a. cathode for producing a. cathode ray, an intensitx c ontml electrode mounted in front 015 the emissivesurface. of said cathode, a. first apertured dia.phragm an electron optica1 preconcentratihg system adapted to produce a first focus: of.=said cathode ray in the aperture of seid firs1r diaphra;gm, said: preconcentra-ting system eonsisting;of; said first. diaphra.gm and two further: apertured diaphragms mounted between said fiislr diaphragm and said control electrode, the apertures: of sa.id three dia.phra.gmg having diacrea;sing diameters in.the direction from said cathbde, the= size= of the* aperture of said first diaphragm being approxianatelyequal to one fifth of the size. of .the. active emissive surface of said caizhode, the diameter 0f thea.perture cf the intermediate: ofsaid three diaphragms being approxilmiately" equa.l to the distance of said intermediae diaphragm: fro'm. said first diaphragm, both being approximately equa:l to' 1 mm.

' KURT SCHLESINGER. 

